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When patients are exposed to ionizing radiation for medical diagnosis or treatment, the procedure being performed should be justified, and the amount of ionizing radiation used should be commensurate with the medical purpose. A legal limit on the amount of ionizing radiation used for medical exposure of a patient does not apply. The biological basis for radiation protection of patients is the same as for all other ionizing radiation exposures: prevent or avoid tissue reactions and reduce the probability of stochastic effects (primarily cancer) while maintaining the benefits to the individual and to society. Justifying the clinical procedure as (1) being appropriate for the clinical purpose and (2) being appropriate for an individual patient is in the purview of the clinical community and individual practitioners, respectively. Managing ionizing radiation levels to be commensurate with the medical purpose is becoming a more prominent feature for all types of imaging procedures (to manage the increased probability of cancer). An approach using advisory diagnostic reference levels is finding widespread use throughout the world. A diagnostic reference level is a method for evaluating whether the amount of radiation is unusually high or low for a particular imaging procedure.

INTRODUCTION

I AM pleased to present the 15th Warren K. Sinclair Keynote Address at this 2018 Annual Meeting of the National Council on Radiation Protection and Measurements (NCRP). I first became involved in NCRP activities in 1988, which was in the latter part of Dr. Sinclair’s tenure as the NCRP president from 1977 through 1991 (and then NCRP president emeritus) and in the midst of his tenure as a main commission member of the International Commission on Radiological Protection (ICRP) from 1977 through 1997 (and then ICRP Main Commission emeritus member). So I was already aware of his many contributions that enhanced the scientific underpinning for radiation protection.

But my fondest Sinclair memory is not that. It goes like this. Each year, Warren and Joy Sinclair would host a get-together at their home in Olney, Maryland. The invitees included NCRP council members and others that served on NCRP committees or otherwise supported NCRP activities. The time frame was the evening, typically from 5 to 8 pm. Fine food was served, and the conversation was stimulating. It was my first attendance, and I was thrilled to be there. Around five minutes to eight, the get-together was still going strong, a couple of attendees had left, and not sure of the proper etiquette, I asked my wife, “Do you think we should leave now?” We hemmed and hawed for a couple of minutes, and exactly at 8 pm, without fanfare or announcement, the Sinclair house lights flashed on and off, then a couple of seconds later on and off, then another couple of seconds later on and off … signaling that the get-together was now over. Without hesitation, we gave our good wishes and said our goodbyes. As we drove away, the house was already dark. The unspoken message … when it’s time to go, it’s time to go. Dare I suggest … when a speaker’s time is up, perhaps flash the house lights (a couple of times if necessary) … and, of course, start with me.

My topic is management of medical exposure of patients to ionizing radiation. The use of ionizing radiation in medicine is pervasive, and from the standpoint of its contribution to the cumulative exposure to the whole population rivals that from the ubiquitous (that is, ever-present, everywhere) natural background radiation. This finding was presented in much detail for the year 2006 in NCRP Report 160 (NCRP 2009). I will not belabor that point other than to say that it is now over a decade later and an update of that contribution (which is likely growing) is underway currently by NCRP.

There are many resources available to help with the task of managing medical exposure to be justified and commensurate with the medical purpose. My purpose here is to advise you of the available resources, in some cases from professional groups that I had nothing to do with (being only a consumer of their product) but find of great value. For those resources, I will try to convey that value. But, I have been more involved in a variety of NCRP reports (seems like forever) and in the activities of ICRP related to protection in medicine even longer. Hopefully, each of you will find something of interest among these resources.

CATEGORIES OF MEDICAL EXPOSURE

Both NCRP and ICRP define three groups of individuals under the overall category of medical exposure that involves ionizing radiation.

Patients: individuals undergoing medical procedures that use ionizing radiation for the purpose of diagnosis, intervention, or therapy. These medical procedures provide a direct benefit to the patient;

Comforters and caregivers: individuals (unpaid and not as an occupation) helping voluntarily at the medical facility and after release from the medical facility in the comfort and care of patients undergoing medical procedures that use ionizing radiation. These individuals are typically parents, other family members, or close friends of the patient; and

Subjects of biomedical research: volunteers taking part in biomedical research that involves ionizing radiation. Biomedical research is defined as studies that involve human subjects conducted to increase fundamental knowledge and understanding of the physical, chemical, and functional mechanisms of human life processes and diseases. These studies usually provide a societal benefit rather than a direct benefit to the volunteer.

CORE MESSAGE ABOUT PATIENTS

When patients are exposed to ionizing radiation for medical diagnosis or treatment the:

Procedure being performed should be justified; and

Amount of ionizing radiation used should be commensurate with the medical purpose.

And a legal limit on the amount of ionizing radiation used for medical exposure of a patient does not apply. Such a limit would do more harm than good. There are suspected or existing chronic, severe, or even life-threatening medical conditions that are more critical than the radiation exposure. Each iteration of patient exposure is a separate assessment (be it informal or formal) to satisfy the condition that the benefit to the patient outweighs the associated radiation-related impact. There are unique aspects of the medical exposure of patients:

Exposure to ionizing radiation is deliberate for an intended outcome; and

Acceptance of the exposure is voluntary with the expectation of direct individual health benefit to the patient exposed.

Go back to the earlier and go forward to the current ICRP and NCRP publications (visit the documents in the listing below)—this core message is consistently found in one form or another.

National Council on Radiation Protection and Measurements

Let’s look at one quote from an earlier time, ICRP Publication 9 (ICRP 1966), paragraph (33): “Concerning the exposure of patients for medical reasons, the Commission believes that it would not be possible to make specific recommendations on dose limitation that would be appropriate for all examinations on individual patients. Nevertheless, the Commission wishes to emphasize the need for limiting the doses from radiological procedures to the minimum amount consistent with the medical benefit to the patient.”

HEALTH EFFECTS RATIONALE

The biological basis for radiation protection of patients is the same as for all other ionizing radiation exposures: there are tissue reactions (deterministic effects) and stochastic effects (primarily cancer).

Tissue reactions occur if the absorbed dose in the relevant tissue is above some threshold, as can happen during radiation therapy or complex fluoroscopically guided interventional procedures. These effects should be prevented, avoided, or when clinically unavoidable should be carefully managed.

There is an increased overall probability of cancer (in a number of different organs and tissues) occurring in an exposed population above the baseline incidence of cancer in the general population.

That increased probability is nonuniformly distributed: some patients are examined much more frequently due to their health status; some groups show higher-than-average sensitivity for cancer induction (e.g., the embryo-fetus, infants and young children [in general], and young females [for breast cancer]);

At mean absorbed doses in organs and tissues (organ doses) above about 100 mGy, the increased probability in a population is generally accepted from the collective epidemiologic evidence, but the magnitude of the increase is not the same for both sexes, or for all ages, tissues, and organs; and

At 100 mGy and below it has not yet been feasible to determine if there is or is not such an increased probability, and the alternative dose-response relationships have been long debated (and continue to be debated).

So that brings me to this somewhat irreverent summary of this everlasting dose-response debate on what happens below about 100 mGy organ dose; that is, below the epidemiologically observed linear portion of the response above 100 mGy. Fig. 1 may look like a cartoon, but it really is to make a point. If at the same time it brings a chuckle or a smile, or even a groan … that is OK too.

And the caption to this lineup says: “The culprit who put us at risk looks somewhat like #2, but could have been #1, or #3, or #4 … or to tell you the truth, it might not be any of them … or it could have been more than one of them … I hope that helps.”

And that is my takeaway from this lineup, assembled in October 1997. It is now March 2018 and I believe the lineup is the same. And each culprit is likely to be guilty under the right set of circumstances.

So … I advance The Rosenstein Proposition, which is:

Whereas, there is an increased probability of cancer in the population at organ doses above about 100 mGy; and

Whereas, organ doses accumulated from medical exposures to a given individual (as a patient) over time often exceed 100 mGy;

It is prudent to properly manage organ doses to all patients at all times.

JUSTIFICATION OF MEDICAL EXPOSURES

Both ICRP (2007a) and NCRP (2018) identify three levels of justification for medical procedures that utilize ionizing radiation:

At the first and most general level, the proper use of ionizing radiation in medicine is accepted as doing more good than harm to society. This general level of justification is now taken for granted;

At the second level, a specified procedure with a specified objective is defined and justified (e.g., chest x rays for patients showing relevant symptoms or a group of individuals at risk for a condition that can be detected and treated). The aim of the second level of justification is to judge whether the radiological procedure will improve the diagnosis or treatment, or will provide necessary information about the exposed individuals; and

At the third level, the application of the procedure to an individual patient should be justified (i.e., the particular application should be judged to do more good than harm to the individual patient). Hence all individual medical exposures should be justified in advance, taking into account the specific objectives of the exposure and the characteristics of the individual involved.

Justifying the clinical procedure as being appropriate for the clinical purpose (level 2) is in the purview of the clinical community, and justifying the clinical procedure as being appropriate for an individual patient (level 3) is in the purview of the individual practitioner.

Extensive efforts have been made to develop guidance for level 2 by the American College of Radiology (ACR) in the United States, the Royal College of Radiologists (RCR) in the United Kingdom, and the European Commission. All three resources provide evidence-based guidelines. I cannot do the content of these resources full justice here, but I encourage you to explore them further, starting at the opening page of their respective websites.

American College of Radiology Appropriateness Criteria® (ACR 2017). Basic access is directly available at https://www.acr.org/Clinical-Resources/ACR-Appropriateness-Criteria. The ACR Appropriateness Criteria® are evidence-based guidelines to assist referring physicians and other providers in making the most appropriate imaging or treatment decision for a specific clinical condition. There is an end user license agreement involved;

Royal College of Radiologists iRefer: Making the Best Use of Clinical Radiology, 8th edition (RCR 2017). Available by subscription at http://www.irefer.org.uk. A synthesis of evidence-based guidelines from the United Kingdom and international sources that provides recommendations for everyday use of clinical imaging services. Use of the iRefer subscription provides the most appropriate imaging investigations for any diagnostic imaging problem; and

Via the basic access link, one can access the ACR Appropriateness Criteria® for diagnostic, interventional, and radiation oncology. Under each of these headings is a list of topics with narrative and rating tables organized by panel. On my most recent visit (22 February 2018), I counted a total of 20 panels (10 under diagnostic, 1 under interventional, and 9 under radiation oncology). In all, there were a total of 253 separate topics. For example, a topic under the Cardiac Panel (under diagnostic) is “chest pain suggestive of acute coronary syndrome.” I give you those numbers just to convey a sense of the scope of coverage there. The medical procedures covered are not limited to only those using ionizing radiation; the procedures include other modalities that do not use ionizing radiation, such as ultrasound and magnetic resonance.

Via the report Radiation Protection 118 (EC 2008), one can access the file in that report of EC Referral Guidelines for Imaging. The file consists of an extensive list of clinical/diagnostic problems organized by category. On my last visit (22 February 2018), I counted a total of 14 categories. In all, there were a total of 335 separate clinical/diagnostic problems. For example, a clinical/diagnostic problem under the cardiovascular category is “Chronic ischemic heart disease and assessment after myocardial infarction.” Again, I give you those numbers just to convey a sense of the scope of coverage there. And again, the medical procedures covered are not limited to only those using ionizing radiation; the procedures include other modalities that do not use ionizing radiation, such as ultrasound and magnetic resonance.

RCR iRefer guidelines are presented in a similar manner as the EC Referral Guidelines but are available by subscription only.

MANAGING EXPOSURES COMMENSURATE WITH THE MEDICAL PURPOSE

And now to managing exposures to be commensurate with the medical purpose.

Once upon a time (way back in the 1950s through 1980s), if an organized and carefully designed survey was made of the amount of radiation needed to perform a given radiological imaging task (say a chest x-ray procedure for a specific clinical purpose) at numerous facilities, it would be almost certain that the distribution of results would be skewed to the high side (Fig. 2). And it was important to gauge also that the image quality was as required, since the amount of radiation used is not the whole story. The majority of results would be bunched in the lower region of values (say 75% of the values) with a continuum of results in the higher region of values and a number of high values that were definite outliers (Fig. 2). Actually, there could even be low values that did not result in an acceptable imaging outcome.

In the United States, the survey typically used specially designed phantoms at each facility that were inserted in the x-ray field with specific directions on what procedure to carry out. In the United Kingdom, the preference was to use actual procedures conducted at each facility on a sample of patients of a reference body habitus. The message in this type of distribution was clear—some of these results indicate poor or improper technique—in the language of this talk; these results were not so commensurate with the medical purpose.

Another universal finding of these efforts over time was: as long as the surveys were conducted and actions taken to identify and correct poor or improper technique, improvement would be observed and maintained. But if the surveys and follow-up ceased, typically because they were not funded fully or other priorities interceded, the overall situation over time would revert to the prior behavior. So constant attention is needed.

Admirable effort has been expended since that once upon a time, and today there is more awareness and commitment to managing radiation exposure of patients to be commensurate with the medical purpose. The imaging equipment now determines and displays the radiation quantities needed to know the amount of radiation used, thanks to the regulators and standards organizations that define, prescribe, or require the needed quantities and to the manufacturers that incorporate them. And professional organizations have coalesced to inform and enlist the medical and dental imaging community on the need to and the methods by which patient exposures are properly managed.

I will touch on a couple of ways to get and stay commensurate with the medical purpose that engages those that are essential to reach: the referring physicians that order the imaging procedures and the imaging professionals (radiologists, technologists, medical physicists) that conduct the procedures.

Know how much radiation is involved relative to the norm—use diagnostic reference levels.

Have an awareness of what the norms are—commit to Image Wisely® (for adult patients) and to Image Gently® (for pediatric patients).

Diagnostic reference levels

The concept of checking the amount of radiation used for medical exposures has been around in the United States since the 1950s and 1960s. Such efforts were already underway by the US Public Health Service (PHS) when I entered the PHS in 1962. ICRP introduced the concept as part of its optimization of protection principle for medical exposure in Publication 60 (ICRP 1991). The term “diagnostic reference level” (DRL) was introduced by ICRP in Publication 73 (ICRP 1996). The use of “diagnostic” at that time was tied to its proposed use as an investigation level for common diagnostic procedures in radiology and nuclear medicine. But I propose the term “diagnostic” be viewed in its more general connotation … to identify the nature of a problem, in this case regardless of the imaging task. So here are the basics for the DRL.

DRL objective

A form of investigation level used in medical imaging with ionizing radiation to indicate whether the amount of radiation used for a specified procedure is unusually high or low for that procedure. The objective is to help avoid delivery of excess radiation to the patient that does not contribute to the clinical purpose of a medical imaging task.

DRL quantity

A commonly obtained measure of the amount of ionizing radiation used to perform a medical imaging task. The quantities selected are those that are readily available for each type of medical imaging modality and medical imaging task. With the single exception of mean breast glandular dose for mammography, these quantities are not the tissue or organ doses received by the patient or quantities derived from such doses, as these doses cannot be measured or determined easily.

DRL value

A numeric value of a DRL quantity, set at the 75th percentile of the distribution of the DRL quantity observed at an appropriate number of facilities performing the medical imaging task:

The numeric value of a DRL is advisory;

The numeric value is not for regulatory or commercial purposes and is not linked to limits or constraints;

The numeric value cannot be applied to individual patients; and

Each numeric value should be tied to defined clinical and technical requirements for the medical imaging task.

I think of the DRL process as a quasi controlled analysis, where the clinical purpose, imaging quality goal, and equipment operating conditions are specified and set for a reference patient in regard to physical characteristics. A reference group of patients is usually defined within a certain range of physical parameters (e.g., height, weight).

Every featured NCRP annual meeting presentation has to include some overwhelming technical and scientific details. So here is my contribution to that fine tradition—the DRL quantities. The word translations of the notations for the DRL quantities are listed below (and for which imaging modalities they are used). My collection here uses the notations recommended by the International Commission on Radiation Units and Measurements (ICRU 2005) or others using the ICRU style of notation:

Those of you who actively work in this field will recognize the quantities and will not be overwhelmed; you are more likely to have personal opinions on what is best to use and what to call it. That’s fine. It is such discussions over the years that have led to further improvements. More details on these quantities are likely to be noted during the rest of the presentations at this meeting. I did not mean to make this a tutorial on the subject. The main point is that different modalities need different quantities.

For those of you whose interest is more general, the take-home message is: Thank goodness he did not try to explain in detail those complex quantities; instead he explained that all these quantities are measures of the amount of radiation applied to the patient for defined equipment, technical settings, and a defined clinical purpose (often referred to as a protocol). He stressed that the purpose is to assess the amount of radiation used against a norm (which is actually a distribution) for the specific protocol.

For those of you that are not technically inclined, the plain language message is: There is considerable effort these days to check whether the imaging procedures that are performed use the correct amount of ionizing radiation to obtain the desired clinical information.

Image Wisely® and Image Gently®

This is all very nice, but how does it get put into practice? How is this advice utilized to influence the behavior of the physicians that order the imaging procedures and the teams of medical staff that conduct the procedures? Glad you asked.

In one case, ACR and the Radiological Society of North America, in collaboration with the American Association of Physicists in Medicine (AAPM) and the American Society of Radiologic Technologists (ASRT) conduct the Image Wisely® campaign tailored to procedures for adult patients. The objective is to lower the amount of radiation used in medically necessary imaging studies and to eliminate unnecessary procedures. Go to the website (just type Image Wisely in your search engine, or go to https://www.imagewisely.org/). You will find resources and information listed:

And my favorite feature on the website: pledges to be renewed annually by imaging professionals, referring practitioners, imaging facilities, and association or education programs that spell out their roles in clear language. I even see references to the concepts of justification and DRLs.

In another focused case, the Society for Pediatric Radiology, in conjunction with the ACR, ASRT, and AAPM, developed the Image Gently® Alliance. The objective is to raise awareness in the imaging community of the need to adjust radiation dose when imaging children, with an ultimate goal of changing practice. This is an international endeavor. When I last looked (22 February 2018), there were 95 alliance organizations listed (United States and international). Go to the website (just type Image Gently in your search engine, or go to http://www.imagegently.org/). You will find information on:

The roles of parents, technologists, dental professionals, physicists, radiologists, and referring physicians in the imaging of children; and

NCRP and ICRP resources

So for those of you who cannot get enough of this subject and have the urge to delve deeper and deeper into the details of one or another of the imaging modalities or related topics, here is a quick roundup of the NCRP and ICRP in-depth resources directly relevant to this presentation. That’s not to say that there are not more resources from NCRP and ICRP not listed that touch on other topics that impact medical exposure to patients. First (of course) is the NCRP collection and then the ICRP collection (since I spent much time with them also).

To access what is available on the NCRP website just type in NCRP publications, then select from reports, commentaries, Taylor Lectures, Sinclair Keynote Addresses, annual meeting proceedings, or symposium proceedings. And see what is already there and how to get the complete documents. To access what is available on the ICRP website just type in ICRP publications, and you will find the complete set and can access the abstracts. The listings below give the: